Three-component photo initiating systems for the red and near infrared

ABSTRACT

The present invention relates to a new photo-initiating composition for red and near infrared-induced photopolymerization, method of using same in photopolymerization reactions and polymers obtained by such method.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a National Stage application of PCT/EP2018/086410, filed Dec. 20, 2018, which claims the benefit of European Application Nos. 18182205.7, filed Jul. 6, 2018 and 17306861.0, filed Dec. 21, 2017, all of which are incorporated by reference in their entirety herein.

FIELD OF THE INVENTION

The present invention relates to a new photo-initiating composition for red and near infrared-induced photopolymerization, method of using same in photopolymerization reactions and polymers obtained by such method.

In what follows, the numbers between brackets ([ ]) refer to the List of References provided at the end of the document.

BACKGROUND OF THE INVENTION

Photopolymerization presents many advantages over conventional thermal polymerization, namely (i) a better spatial and temporal control of the polymerization reaction; (ii) a polymerization that can be carried out in the absence of solvent and (iii) under milder conditions (irradiation instead of heating); thereby being advantageous in terms of economic and energetic costs. For these reasons, light induced free radical polymerization reactions using a photoinitiator (PI) or a photo-initiating system (PIS) have been largely studied in the past few years. In addition, they find applications in many industrial fields such as coatings, paints, dentistry, medicine and 3D printing.

So far, most of the compositions used in photopolymerization require high or low intensity UV lamps. Currently, UV-curing is mostly used for the photopolymerization of methacrylate monomers. Because UV wavelengths are known to cause skin and eye damage, a great challenge is to develop new free radical initiating systems that are workable under longer (safer) wavelength irradiation. Additional drawbacks of UV-induced or visible light-induced photopolymerization include limitations in the thickness of sample to be polymerized (polymerization of thin layers only), use of a high quantity if photoinitiator system, and/or necessity to conduct the photopolymerization under inert conditions (CO₂, N₂, . . .).

Therefore, there remains a need for the development of new photoinitiator systems that efficiently trigger photopolymerization under mild light irradiation, and that allow polymerization to be carried out in depth through thick samples/materials.

BRIEF DESCRIPTION OF THE DRAWINGS

In the Figures where it appears, the

symbol signifies that irradiation starts.

Likewise in all the Figures and associated legends below, “Ar₂I⁺/PF₆ ⁻” refers to the following iodonium salt:

FIG. 1 . UV-vis diffusion of light for a polystyrene latex (112 nm of average diameter) and calculated penetrations of selected photons.

FIG. 2 . RT-FTIR spectra of methacrylate monomer between 4500 nm and 7500 nm (1) before polymerization (2) after polymerization. Circled is the peak representative of the double bond C═C conversion used to calculate the photopolymerization profile (methacrylate function conversion vs. irradiation time).

FIG. 3 . Photopolymerization profiles of Mix-MA under air (methacrylates function conversion vs. irradiation time) in the presence of (1) IR140-borate (0.1 w %), (2) IR140-borate/Ar₂I⁺/PF₆ ⁻ (0.1 w %/3 w %), (3) IR140-borate/Ar₂I⁺/PF₆ ⁻/4-dppba (0.1 w %/3 w %/2 w %); (4) monomer alone under exposure to laser@785 nm, 400 mW/cm² (5) IR140-borate/Ar₂I⁺/PF₆ ⁻/4-dppba (0.1 w %/3 w %/2 w %); laser@785 nm, 2.55 W/cm²; thickness=1.4 mm. The irradiation started at t=17 s.

FIG. 4 . Photopolymerization profiles of Mix-MA under air (methacrylates function conversion vs. irradiation time) in the presence of IR 140-borate (0.1 w %), Ar₂I⁺/PF₆ ⁻ (3 w %) and 4-dppba (2 w %); Laser@785 nm; thickness=1.4 mm; (1) 0.4 W/cm², (2) 1.37 W/cm², (3) 1.82 W/cm², (4) 2.08 W/cm², (5) 2.34 W/cm², (6) 2.55 W/cm² The irradiation started at t=17 s.

FIG. 5 . Photopolymerization of Mix-MA under air (methacrylates function conversion vs. irradiation time) in the presence of IR 140-borate/Ar₂I⁺/PF₆ ⁻/4-dppba (0.1 w %/3 w %/2 w %) and different fillers rate; Laser@785 nm, 2.55 W/cm²; (A) profiles with (1) 0 w % of fillers, (2) 25 w % of fillers, (3) 50 w % of fillers, (4) 75 w % of fillers thickness=1.4 mm; photography with 75 w % fillers (B) composite for a thickness=1 cm (C) composite for a thickness=1.4 mm. The irradiation started at t=17 s.

FIG. 6 . Photopolymerization profiles of Mix-MA under air (methacrylates function conversion vs. irradiation time) in the presence of 3 w % Ar₂I⁺/PF₆ ⁻, 2 w % 4 dppba and 0,1 w % (1) IR140-borate, (2) Indocyanine Green, (3) IR813 p-toluenesulfonate, (4) IR780-borate, (5) Manganese (II) phthalocyanine (Mn-Ph), (6) chlorophyllin copper sodium salt, and (7) Dithiolene Nickel 1, under exposure to (A) LED@660 nm, (B) Laser@785 nm, 400 mW/cm², (C) Laser@785 nm, 2.55 W/cm²; thickness=1.4 mm. The irradiation started at t=17 s.

FIG. 7 . Photopolymerization profiles of Mix-MA under air (methacrylates function conversion vs. irradiation time) in the presence of Ar₂I⁺/PF₆ ⁻ (3 w %), 4-dppba (2 w %) and IR-140 (0.1 w %); (1) commercial; (2) borate; under exposure to Laser@785 nm, 2.55 W/cm²; under air; thickness=1.4 mm. The irradiation started at t=17 s.

FIG. 8 . Photopolymerization profiles of Mix-MA under air (methacrylates function conversion vs. irradiation time) in the presence of Ar₂I⁺/PF₆ ⁻ (3 w %), 4-dppba (2 w %) and (1) IR-140 borate (0.1 w %) (2) S2265 (0.1 w %) under exposure to Laser@785 nm, 2.55 W/cm²; thickness=1.4 mm. The irradiation started at t=17 s.

FIG. 9A. Photopolymerization profiles of Mix-MA under air (methacrylates function conversion vs. irradiation time) in the presence of Ar₂I⁺/PF₆ ⁻ (3 w %), NPG (2 w %) and (1) IR 783 (0.1 w %), (2) IR 783 (0.1 w %), (3) IR 813 (0.1 w %), (4) indocyanine green (0.1w %), (5) IR 780 (0.1 w %) and (6) IR-140 borate (0.1 w %) under exposure to Laser@785 nm, I=2.5 W/cm²; thickness=1.4 mm. The irradiation started at t=15 s.

FIG. 9B. Photopolymerization profiles of Mix-MA under air (methacrylates function conversion vs. irradiation time) in the presence of Ar₂I⁺/PF₆ ⁻ (3 w %), DABA (2 w %) and (1) IR 783 (0.1 w %), (2) IR 783 (0.1 w %), (3) IR 813 (0.1 w %), (4) indocyanine green (0.1 w %), (5) IR 780 (0.1 w %) and (6) IR-140 borate (0.1 w %) under exposure to Laser@785 nm, I=2.5 W/cm²; thickness=1.4 mm. The irradiation started at t=15 s.

DEFINITIONS

To facilitate an understanding of the present invention, a number of terms and phrases are defined below:

As used herein other than the claims, the terms “a,” “an,” “the,” and/or “said” means one or more. As used herein in the claim(s), when used in conjunction with the words “comprise,” “comprises” and/or “comprising,” the words “a,” “an,” “the,” and/or “said” may mean one or more than one. As used herein and in the claims, the terms “having,” “has,” “is,” “have,” “including,” “includes,” and/or “include” has the same meaning as “comprising,” “comprises,” and “comprise.” As used herein and in the claims “another” may mean at least a second or more.

The phrase “a mixture thereof” and such like following a listing, the use of “and/or” as part of a listing, a listing in a table, the use of “etc” as part of a listing, the phrase “such as,” and/or a listing within brackets with “e.g.,” or i.e., refers to any combination (e.g., any sub-set) of a set of listed components, and combinations and/or mixtures of related species and/or embodiments described herein though not directly placed in such a listing are also contemplated. Such related and/or like genera(s), sub-genera(s), specie(s), and/or embodiment(s) described herein are contemplated both in the form of an individual component that may be claimed, as well as a mixture and/or a combination that may be described in the claims as “at least one selected from,” “a mixture thereof” and/or “a combination thereof.”

In general, the term “substituted” whether preceded by the term “optionally” or not, and substituents contained in formulae of this invention, refer to the replacement of hydrogen radicals in a given structure with the radical of a specified substituent. When more than one position in any given structure may be substituted with more than one substituent selected from a specified group, the substituent may be either the same or different at every position. As used herein, the term “substituted” is contemplated to include all permissible substituents of organic compounds.

The term “aliphatic”, as used herein, includes both saturated and unsaturated, straight chain (i.e., unbranched) or branched aliphatic hydrocarbons, which are optionally substituted with one or more functional groups. As will be appreciated by one of ordinary skill in the art, “aliphatic” is intended herein to include, but is not limited to, alkyl, alkenyl, alkynyl moieties.

As used herein, the term “alkyl”, refers to straight and branched alkyl groups. An analogous convention applies to other generic terms such as “alkenyl”, “alkynyl” and the like. As used herein, “lower alkyl” is used to indicate those alkyl groups (substituted, unsubstituted, branched or unbranched) having about 1-6 carbon atoms. Illustrative alkyl groups include, but are not limited to, for example, methyl, ethyl, n-propyl, isopropyl, allyl, n-butyl, sec-butyl, isobutyl, tert-butyl, n-pentyl, sec-pentyl, isopentyl, tert-pentyl, n-hexyl, sec-hexyl, moieties and the like, which again, may bear one or more substituents. Alkenyl groups include, but are not limited to, for example, ethenyl, propenyl, butenyl, 1-methyl-2-buten-1-yl, and the like. Representative alkynyl groups include, but are not limited to, ethynyl, 2-propynyl (propargyl), 1-propynyl and the like.

The term “alicyclic”, as used herein, refers to compounds which combine the properties of aliphatic and cyclic compounds and include but are not limited to cyclic, or polycyclic aliphatic hydrocarbons and bridged cycloalkyl compounds, which are optionally substituted with one or more functional groups. As will be appreciated by one of ordinary skill in the art, “alicyclic” is intended herein to include, but is not limited to, cycloalkyl, cycloalkenyl, and cycloalkynyl moieties, which are optionally substituted with one or more functional groups. Illustrative alicyclic groups thus include, but are not limited to, for example, cyclopropyl, —CH₂-cyclopropyl, cyclobutyl, —CH₂-cyclobutyl, cyclopentyl, —CH₂-cyclopentyl-n, cyclohexyl, —CH₂-cyclohexyl, cyclohexenylethyl, cyclohexanylethyl, norborbyl moieties and the like, which again, may bear one or more substituents.

The term “cycloalkyl”, as used herein, refers specifically to cyclic alkyl groups having three to seven, preferably three to ten carbon atoms. Suitable cycloalkyls include, but are not limited to cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl and the like, which, as in the case of aliphatic, heteroaliphatic or heterocyclic moieties, may optionally be substituted. An analogous convention applies to other generic terms such as “cycloalkenyl”, “cycloalkynyl” and the like.

The term “heteroaliphatic”, as used herein, refers to aliphatic moieties in which one or more carbon atoms in the main chain have been substituted with a heteroatom. Thus, a heteroaliphatic group refers to an aliphatic chain which contains one or more oxygen, sulfur, nitrogen, phosphorus or silicon atoms, i.e., in place of carbon atoms. Heteroaliphatic moieties may be branched or linear unbranched. An analogous convention applies to other generic terms such as “heteroalkyl”, “heteroalkenyl”, “heteroalkynyl” and the like.

The term “heterocyclic” or “heterocycle”, as used herein, refers to compounds which combine the properties of heteroaliphatic and cyclic compounds and include but are not limited to saturated and unsaturated mono- or polycyclic heterocycles such as morpholino, pyrrolidinyl, furanyl, thiofuranyl, pyrrolyl etc., which are optionally substituted with one or more functional groups, as defined herein. In certain embodiments, the term “heterocyclic” refers to a non-aromatic 5-, 6- or 7- membered ring or a polycyclic group, including, but not limited to a bi- or tri-cyclic group comprising fused six-membered rings having between one and three heteroatoms independently selected from oxygen, sulfur and nitrogen, wherein (i) each 5-membered ring has 0 to 2 double bonds and each 6-membered ring has 0 to 2 double bonds, (ii) the nitrogen and sulfur heteroatoms may optionally be oxidized, (iii) the nitrogen heteroatom may optionally be quaternized, and (iv) any of the above heterocyclic rings may be fused to an aryl or heteroaryl ring. Representative heterocycles include, but are not limited to, pyrrolidinyl, pyrazolinyl, pyrazolidinyl, imidazolinyl, imidazolidinyl, piperidinyl, piperazinyl, oxazolidinyl, isoxazolidinyl, morpholinyl, thiazolidinyl, isothiazolidinyl, and tetrahydrofuryl.

In general, the term “aromatic moiety” or “aryl”, as used herein, refers to stable substituted or unsubstituted unsaturated mono- or polycyclic hydrocarbon moieties having preferably 3-14 carbon atoms, comprising at least one ring satisfying the Hückel rule for aromaticity. Examples of aromatic moieties include, but are not limited to, phenyl, indanyl, indenyl, naphthyl, phenanthryl and anthracyl.

As used herein, the term “heteroaryl moiety” refers to unsaturated mono-heterocyclic or polyheterocyclic moieties having preferably 3-14 carbon atoms and at least one ring atom selected from S, O and N, comprising at least one ring satisfying the Hückel rule for aromaticity. The term “heteroaryl” refers to a cyclic unsaturated radical having from about five to about ten ring atoms of which one ring atom is selected from S, O and N; zero, one or two ring atoms are additional heteroatoms independently selected from S, O and N; and the remaining ring atoms are carbon, the radical being joined to the rest of the molecule via any of the ring atoms, such as, for example, pyridyl, pyrazinyl, pyrimidinyl, pyrrolyl, pyrazolyl, imidazolyl, thiazolyl, oxazolyl, isooxazolyl, thiadiazolyl, oxadiazolyl, thiophenyl, furanyl, quinolinyl, isoquinolinyl, and the like. Examples of heteroaryl moieties include, but are not limited to, pyridyl, quinolinyl, dihydroquinolinyl, isoquinolinyl, quinazolinyl, dihydroquinazolyl, and tetrahydroquinazolyl.

As used herein, the expression “C_(x)-C_(y), preferably C_(x1)-C_(y1), alkylaryl, aralkyl or aryl”, where x, y, x1 and y1 represent integers denoting the number of carbon atoms in the chemical moiety to which it refers (e.g., “alkylaryl”, “aralkyl”, “aryl”)), means “C_(x)-C_(y)alkylaryl, C_(x)-C_(y)aralkyl or C_(x)-C_(y)aryl, preferably C_(x1)-C_(y1)alkylaryl, C_(x1)-C_(y1)aralkyl or C_(x1)-C_(y1)aryl”. Likewise, the expression “C_(x)-C_(y) alkylaryl, aralkyl or aryl”, means “C_(x)-C_(y)alkylaryl, C_(x)-C_(y)aralkyl or C_(x)-C_(y)aryl”.

The term “halogen” as used herein refers to an atom selected from fluorine, chlorine, bromine and iodine.

The term “amine” refers to a group having the structure —N(R)₂ wherein each occurrence of R is independently hydrogen, or an aliphatic, heteroaliphatic, aryl or heteroaryl moiety, or the R groups, taken together with the nitrogen atom to which they are attached, may form a heterocyclic moiety.

As used herein, the term “independently” refers to the fact that the substituents, atoms or moieties to which these terms refer, are selected from the list of variables independently from each other (i.e., they may be identical or the same).

As used herein, the term “mild light irradiation conditions” or “mild irradiation conditions” refers to irradiation conditions in the near infrared region e.g., λ=625-2500 nm, for example under near infrared light range λ=700-2500 nm, in particular in the near infrared light range λ=700-1500 nm, with low intensity of a few W/cm² or even in the mW/cm² range. For example the near infrared irradiation intensity may range from 50 mW/cm² to 10 W/cm², advantageously from 100 mW/cm² to 7 W/cm², more advantageously from 200 mW/cm² to 5 W/cm², still more advantageously from 300 mW/cm² to 3 W/cm².

As used herein and in the claims, “about” refers to any inherent measurement error or a rounding of digits for a value (e.g., a measured value, calculated value such as a ratio), and thus the term “about” may be used with any value and/or range. As used herein, the term “about” can refer to a variation of ±5%, ±10%,±20%, or ±25%, of the value specified. For example, “about 50” percent can in some embodiments carry a variation from 45 to 55 percent. For integer ranges, the term “about” can include one or two integers greater than and/or less than a recited integer. Unless indicated otherwise herein, the term “about” is intended to include values, e.g., weight percents, proximate to the recited range that are equivalent in terms of the functionality of the individual ingredient, the composition, or the embodiment.

As used herein, the term “and/or” means any one of the items, any combination of the items, or all of the items with which this term is associated.

As will be understood by the skilled artisan, all numbers, including those expressing quantities of ingredients, properties such as molecular weight, reaction conditions, and so forth, are approximations and are understood as being optionally modified in all instances by the term “about.” These values can vary depending upon the desired properties sought to be obtained by those skilled in the art utilizing the teachings of the descriptions herein. It is also understood that such values inherently contain variability necessarily resulting from the standard deviations found in their respective testing measurements.

As will be understood by one skilled in the art, for any and all purposes, particularly in terms of providing a written description, all ranges recited herein also encompass any and all possible subranges and combinations of subranges thereof, as well as the individual values making up the range, particularly integer values. A recited range (e.g., weight percents or carbon groups) includes each specific value, integer, decimal, or identity within the range. Any listed range can be easily recognized as sufficiently describing and enabling the same range being broken down into at least equal halves, thirds, quarters, fifths, or tenths. As a non-limiting example, each range discussed herein can be readily broken down into a lower third, middle third and upper third, etc.

As will also be understood by one skilled in the art, all language such as “up to,” “at least,” “greater than,” “less than,” “more than,” “or more,” and the like, include the number recited and such terms refer to ranges that can be subsequently broken down into subranges as discussed above. In the same manner, all ratios recited herein also include all subratios falling within the broader ratio. Accordingly, specific values recited for radicals, substituents, and ranges, are for illustration only; they do not exclude other defined values or other values within defined ranges for radicals and substituents.

One skilled in the art will also readily recognize that where members are grouped together in a common manner, such as in a Markush group, the invention encompasses not only the entire group listed as a whole, but each member of the group individually and all possible subgroups of the main group. Additionally, for all purposes, the invention encompasses not only the main group, but also the main group absent one or more of the group members. The invention therefore envisages the explicit exclusion of any one or more of members of a recited group. Accordingly, provisos may apply to any of the disclosed categories or embodiments whereby any one or more of the recited elements, species, or embodiments, may be excluded from such categories or embodiments, for example, as used in an explicit negative limitation.

DETAILED DESCRIPTION OF CERTAIN PREFERRED EMBODIMENTS OF THE INVENTION

As noted above, there has been increasing interest in recent years in the development of new photoinitiator systems that efficiently trigger photopolymerization under mild light irradiation, for example in the red to near-infrared region. Thus far, only a few studies have reported near-infrared-induced (“NIR-induced”) photopolymerization. However, only a few studies have been reported so far. [1, 2, 3] For example, the curing of NIR photo-initiating system using a cyanine-based dye has been reported.[3] However, the use of NIR photo-initiating systems (e.g. cyanine) is typically associated with a low reactivity (low conversion and/or reaction rate(s)) and requiring high light intensity. For that reason, such NIR-photoinitiator systems are typically not suitable for most practical/industrial applications, notably for those applications where mild intensity irradiation is required.

The inventors have discovered that a properly selected three-component photoinitiator system can overcome the aforementioned drawbacks in the field.

In this context, there is provided herein a photo-initiating composition comprising:

-   -   (a) an absorbing dye that is an electron donor when exposed to a         625-2500 nm light source;     -   (b) an oxidizing agent suitable for a polymerization reaction         and capable of generating free radicals and/or cation ions by         electron transfer from the dye when exposed to a 625-2500 nm         light source;     -   (c) a reducing agent suitable for regenerating the dye; and     -   (d) optionally, an oxygen scavenger.

Briefly, the present invention relates to the association of three components as a photoinitiator system for the red to near infrared (NIR) photopolymerization, preferably NIR-induced photopolymerization. The three-component association is based on: 1) an absorbing dye used as a photosensitizer in the red to NIR range, preferably the NIR range, 2) an oxidizing agent capable of generating free radicals and/or cation ions by electron transfer from the absorbing dye when exposed to a 625-2500 nm light source and 3) a reducing agent suitable for regenerating the absorbing dye.

Advantageously, the photoinitiator system may additionally comprise an oxygen scavenger suitable for reducing and/or preventing oxygen inhibition during the free radical polymerization.

a) Absorbing Dye

Advantageously, the absorbing dye may be any suitable dye that is an electron donor when exposed to a 625-2500 nm light source (i.e., when exposed to irradiation in the red to near-infrared), for example when exposed to a 625-1500 nm light irradiation.

Advantageously, the absorbing dye may comprise a cyclic or acyclic conjugated system containing 2 or 4 heteroatoms selected from N or S the lone pair of which may participate in the conjugated system; wherein the absorbing dye is an electron donor when exposed to a 625-2500 nm light source, for example when exposed to a 625-1500 nm light irradiation.

Advantageously, the absorbing dye may comprise:

-   -   an opened conjugated system containing two N or S atoms,         preferably two N atoms, the lone pairs of which may participate         in the conjugated system;     -   a conjugated macrocyclic system containing four N or S atoms,         preferably four N atoms, complexed to a single metal atom;         preferably a metal atom that absorbs in the red to near-infrared         region of 625-2500 nm, for example a metal atom that absorbs in         the range 625-1500 nm;     -   a metal complex comprising two bidentate conjugated ligands;         each bidentate ligand containing two N or S atoms, preferably         two S atoms, complexed to a single metal atom; preferably a         metal atom that absorbs in the red to near-infrared region of         625-2500 nm, for example a metal atom that absorbs in the range         625-1500 nm.

Advantageously, the absorbing dye may be selected from cyanine, phthalocyanine, dithiolene or porphyrin dyes.

As used herein, the term “cyanine dye” does not deviate from the conventional meaning of the term in the art, and refers to a dye having an opened conjugated system where a moiety

and a moiety

are covalently linked via a conjugated system of two or more double bonds, some of which may belong to an aromatic radical. The expression “opened conjugated system” refers to the fact that the moieties

do not form a cycle together with the conjugated double bonds (i.e;, the whole does not piggy-back together to form a cycle). However, the whole system may comprise one or more mono- or polycyclic alicyclic, heterocyclic, aromatic or heteroaromatic radicals.

Examples of such cyanine dyes include:

wherein X⁻ represents a suitable counterion. For example, X⁻ may represent Cl⁻, I⁻, ClO₄ ⁻, p-toluenesulfonate, p-dodecylbenzenesulfonate, or a borate anion, such as triphenylbutylborate.

Advantageously, the counterion X⁻ may represent a borate anion. For example X⁻ may represent triphenylbutylborate.

For example, any one or more of the following cyanine dyes may be used as absorbing dye:

As used herein, the term “phthalocyanine dye” does not deviate from the conventional meaning of the term in the art, and refers to conjugated macrocycles which, depending on how they were synthesized, contain different metal or metalloid inclusions. Advantageously, a phthalocyanine dye useable in the context of the present invention may have a cyclic conjugated system having the structure:

wherein M represents a metal center, for example Mn, and L₁ and L₂ independently represent acyloyl ligands or may be absent, depending on the metal atom valency.

Examples of such phthalocyanine dyes include:

Most phthalocyanines (Pcs) have a high molar absorptivity coefficient and absorb light in the red and near infra-red (NIR) region (≈650-700 nm [4, 6]).

Incidentally, NIR dyes and more specifically, borate dyes, have also been used for information recording such as xerography, a dry photoprinting technique.

When the cyanine borate dye is photoirradiated, electron transfer between the dye and the counter ion allows a recombination of dye radical to give a colorless dye. This process facilitates the bleaching, and ultimately, the recycling of the paper several times. This bleaching property can also be very interesting for photopolymerization. Going from green to colorless while polymerizing, light can penetrate deeper in the sample and so thicker samples can be polymerized.

As used herein, the term “dithiolene dye” does not deviate from the conventional meaning of the term in the art, and refers to metal complexes including unsaturated bidentate ligands containing two sulfur donor atoms. They may be also referred to as “metallodithiolene dyes”. Advantageously, a dithiolene dye useable in the context of the present invention may have the structure:

wherein M represents a metal center that absorbs in the red to near-infrared region of 625-2500 nm, for example a metal atom that absorbs in the range 625-1500 nm, such as Ni; and Ar₁, Ar₂, Ar₃, and Ar₄ independently represent a C₆₋₁₀ aryl; wherein each aryl moiety may be, individually, further substituted with one or more substituents, such as —OH, —OR, halogen atom, —NO₂, —CN, —NR^(A) ₁R^(A) ₂, —NHC(═O)R^(A) ₃, —OC(═O)R^(A) ₃, vinyl, or linear or branched C₁₋₁₀alkyl or C₆₋₁₀ aryl moieties; wherein R and R^(A) ₃ independently represent a linear or branched C₁₋₁₀ alkyl or C₆₋₁₀ aryl moiety; and R^(A) ₁ and R^(A) ₂ independently represent H or linear or branched C₁₋₆ alkyl or C₆₋₁₀ aryl moieties, where R^(A) ₁ and R^(A) ₂, taken together with the nitrogen atom to which they are attached, may form a 5- or 6-membered heterocyclic moiety; wherein each of the foregoing aryl moieties may be, individually, further substituted with one or more linear or branched C₁₋₆ alkyl or C₆₋₁₀ aryl moieties. Advantageously, Ar₁, Ar₂, Ar₃, and Ar₄ may independently represent a phenyl moiety; wherein each phenyl moiety may be, individually, further substituted with one or more substituents, such as those as described immediately above, preferably linear or branched C₁₋₆alkyl moieties, including methyl, propyl, butyl, i-propyl.

Examples of such dithiolene dyes include:

As used herein, the term “porphyrin dye” does not deviate from the conventional meaning of the term in the art, and refers to conjugated heterocyclic macrocycle metal complexes comprising four modified pyrrole subunits interconnected at their □ carbon atoms via methine bridges (═CH—).

Advantageously, a porphyrin dye useable in the context of the present invention may have a heterocyclic conjugated system having the structure:

wherein M represents a metal center that absorbs in the red to near-infrared region of 625-2500 nm, for example a metal atom that absorbs in the range 625-1500 nm, such as Mg or Cu; and each occurrence of R₁, R₂, R₃, and R₄ may independently represent H, —C(═O)OR₅, vinyl, a linear or branched C₁₋₁₀ alkyl or a C₆₋₁₀ aryl moiety; wherein R₅, for each occurrence, may independently represent H or an alkali metal cation such as Na⁺; and wherein each of the foregoing alkyl or aryl moieties may be, individually, further substituted with one or more linear or branched C₁₋₆ alkyl or C₆₋₁₀ aryl moieties.

Examples of such porphyrin dyes include chlorophyllin sodium copper salt:

Advantageously, the adsorbing dye may be used in about 0.01-0.5 wt %, preferably 0.01-0.4 wt %, preferably 0.01-0.3 wt %, more preferably ≤0.25 wt %, still more preferably ≤0.20 wt %, most preferably ≤0.15 wt %, based on the total weight of the composition to be polymerized; i.e. total weight of polymerizable component+total weight of components a), b) and c) recited above. For example the adsorbing dye may be used in about 0.05 wt %, 0.06 wt %, 0.07 wt %, 0.08 wt %, 0.09 wt %, 0.10 wt %, 0.11 wt %, 0.12 wt %, 0.13 wt %, 0.14 wt %, 0.15 wt %, 0.16 wt %, 0.17 wt %, 0.18 wt %, 0.19 wt %, 0.20 wt %, based on the total weight of the composition to be polymerized; i.e. total weight of polymerizable component+total weight of components a), b) and c) recited above.

b) Oxidizing Agent

The oxidizing agent may be selected from any suitable oxidizing agent known in the field of polymerization. For example, the oxidizing agent may be an onium salt (for example an iodonium or a sulfonium salt of formula (R_(A))₂I⁺X_(A) ⁻ or (R_(A))₃S⁺X_(A) ⁻; wherein each occurrence of R_(A) independently represents a C₆₋₁₀ aryl or a C₁₋₁₀ alkyl moiety; wherein each aryl moiety may be, individually, further substituted with one or more linear or branched C₁₋₆ alkyl or C₆₋₁₀ aryl moieties; and X_(A) ⁻ represents a suitable counterion). For example each occurrence of R_(A) may independently represent a phenyl or a C₁₋₁₀ alkyl moiety; wherein each phenyl moiety may be, individually, further substituted with one or more linear or branched C₁₋₆ alkyl or C₆₋₁₀ aryl moieties. For example, the phenyl moiety may bear one or more methyl, ethyl, n-propyl, i-propyl, t-butyl groups, preferably in para position relative to the iodine atom. In exemplary embodiments, X_(A) ⁻ may represent B(PhF₆)₄ ⁻, PF₆ ⁻, SbF₆ ⁻ or Cl⁻. Preferably, X_(A) ⁻ may represent B(PhF₆)₄ ⁻ or PF₆ ⁻, most preferably B(PhF₆)₄ ⁻.

Advantageously, the oxidizing agent may be an iodonium salt of formula (R_(A))₂I⁺X_(A) ⁻, as defined and described in any variant above and herein. Advantageously, the oxidizing agent may be:

Advantageously, the oxidizing agent may be used in about 0.1-5.0 wt %, preferably 0.5-5.0 wt %, preferably 0.5-4.0 wt %, more preferably 1-4.0 wt %, still more preferably 2.0-4.0 wt %, most preferably about 3 wt %, based on the total weight of the composition to be polymerized; i.e. total weight of polymerizable component+total weight of components a), b) and c) recited above. For example the oxidizing agent may be used in about 0.5 wt %, 1.0 wt %, 1.5 wt %, 2.0 wt %, 2.5 wt %, 3.0 wt %, 3.5 wt %, 4.0 wt %, 4.5 wt %, 5.0 wt %, based on the total weight of the composition to be polymerized; i.e. total weight of polymerizable component+total weight of components a), b) and c) recited above.

c) Reducing Agent

Advantageously, the reducing agent (c) may be any reducing agent suitable for regenerating the absorbing dye (a). In the initial stages of the photo-initiating process, the dye (electron donor when exposed to a 625-2500 nm light source, for example when exposed to a 625-1500 nm light irradiation) absorbs in the red-NIR range to release an electron and form a radical dye^(⋅+). The expression “regenerate the absorbing dye (a)”, as used in the context of the present invention, refers to the process of reverting a dye^(⋅+) radical back to the initial neutral dye molecule.

As such, advantageously, the reducing agent (RA) may preferably be able to revert dye^(⋅+) radicals back to the initial neutral dye molecules, as follows:

Examples of suitable reducing agents include phosphine compounds/phosphine-based reducing agents (for example 4-(diphenylphosphino)benzoic acid (4-dppba), 2-diphenylphosphinobenzoic acid (2-dppba), bis(2-diphenylphosphinophenyl)-ether (2-dpppe), triomethoxyphenylphosphine (triompp), DPBP bidentate phosphine (DPBP), 4-dimethylaminophenyldiphenylphosphine (4-dmapdp), (R,R) dach phenyl trost (trost), triphenylphosphine (tpp)); and amine compounds/amine-based reducing agents (for example Ethyl 4-dimethylaminobenzoate (EDB), 4-(dimethylamino)phenylacetic acid (ADP), triphenylamine (TPA), N,N-dibutylaniline (DBA), N-Ethyl-N-isopropylaniline (EIPA), 3-(dimethylamino)benzyl alcohol (3-dmaba or “DABA”)). Other suitable amine-based reducing agents include N-phenyl glycine or other aromatic amines.

Advantageously, the reducing agent (c) may be a phosphine-based reducing agent from the class P(R_(B1))₃, wherein each occurrence of R_(B1) independently represents a C₆₋₁₀ aryl; wherein any of the foregoing aryl moieties may be independently further substituted with one or more —C(═O)OH, —C(═O)OR_(B2), or a linear or branched C₁₋₆ alkyl or C₆₋₁₀ aryl moieties; wherein R_(B2) independently represents a C₆₋₁₀ aryl or a C₁₋₁₀ alkyl moiety. Advantageously, the reducing agent (c) may be from the class (Ph)₂PR_(B1), wherein R_(B1) independently represents a C₆₋₁₀ aryl moiety optionally further substituted with one or more —C(═O)OH, —C(═O)OR_(B2), or a linear or branched C₁₋₆ alkyl or C₆₋₁₀ aryl moieties; wherein R_(B2) independently represents a C6-10 aryl or a C₁₋₁₀ alkyl moiety. Preferably the reducing agent (c) may be from the class (Ph)₂PR_(B1), wherein R_(B1) represents a C₆ aryl moiety bearing one or more C(═O)OH or —C(═O)OR_(B2) moieties, wherein R_(B2) independently represents a C₆₋₁₀ aryl or a C₁₋₁₀ alkyl moiety. For example, the reducing agent (c) may be 4-(diphenylphosphino)benzoic acid (4-dppba).

Advantageously, the reducing agent (c) may be an aromatic amine-based compound having the structure:

wherein

n represents an integer from 0 to 3, preferably 0-2, most preferably 0 or 1;

R₆ and R₇ may independently represent H, C1-6alkyl or —C1-6alkylC(═O)OR₉, where R₉ represents H or C1-6alkyl; and

R₈ may independently represent —C1-6alkyl-OH or —C1-6alkylC(═O)OR₁₀, where R₁₀ represents H or C1-6alkyl.

Advantageously, at least one of R₆ or R₇ is not H.

Advantageously, n may represent 0, R₆ may represent H and R₇ may represent —C1-6alkylC(═O)OR₉, where R₉ represents H or C1-6alkyl.

Advantageously, n may represent 1, R₈ may represent —C1-6alkyl-OH, and R₆ and R₇ may independently represent C1-6alkyl.

Advantageously, the reducing agent (c) may be NPG or DABA:

Advantageously, the reducing agent may be used in about 0.1-5.0 wt %, preferably 0.5-5.0 wt %, preferably 0.5-4.0 wt %, more preferably 1.0-4.0 wt %, still more preferably 1.0-3.0 wt %, most preferably about 2 wt %, based on the total weight of the composition to be polymerized; i.e. total weight of polymerizable component+total weight of components a), b) and c) recited above. For example the oxidizing agent may be used in about 0.5 wt %, 1.0 wt %, 1.5 wt %, 2.0 wt %, 2.5 wt %, 3.0 wt %, 3.5 wt %, 4.0 wt %, 4.5 wt %, 5.0 wt %, based on the total weight of the composition to be polymerized; i.e. total weight of polymerizable component+total weight of components a), b) and c) recited above.

d) Oxygen Scavenger

Advantageously, an oxygen scavenger may be used in the photo-initiating composition according to the invention to facilitate polymerization in cases where unwanted peroxide radicals are formed during the polymerization process (for example when the polymerization is carried in the presence of oxygen gas (e.g., under air or ambient atmosphere). Advantageously, when an oxygen scavenger is used it should be compatible with the photopolymerization reaction that is intended (free radical, cationic or dual free radical/cationic): it preferably does not interfere with active species that promote the type of polymerization reaction that is being carried out. For example, the oxygen scavenger preferably does not interfere with free radical formation and/or cation formation.

For example, when polymerization is performed under air, certain monomers (such as methacrylates) may be sensitive to the oxygen present in the air. In such cases, peroxyl radicals may be generated in the course of polymerization that are too stable to allow polymerization to proceed (in other words, polymerization is inhibited). The oxygen scavenger helps to overcome oxygen inhibition by reacting with the peroxyl radicals to yield less stable radicals, which in turn can allow for the polymerization to proceed/continue. Any commonly used oxygen scavenger for facilitating polymerization may be further used as part of the photo-initiating composition of the invention. Examples of such oxygen scavengers include potassium sulfite, unsaturated hydrocarbons, and ascorbic acid derivatives.

Advantageously, the reducing agent (c) and the oxygen scavenger (d) may be a single compound (in other words, the same compound may serve as reducing agent (c) and oxygen scavenger (d)). For example, any one of the phosphine reducing agents described in section c) above may also function as oxygen scavenger. As such, advantageously, the oxygen scavenger (d) may be a phosphine-based compound from the class P(R_(B1))₃, wherein each occurrence of R_(B1) independently represents a C₆₋₁₀ aryl; wherein any of the foregoing aryl moieties may be independently further substituted with one or more —C(═O)OH, —C(═O)OR_(B2), or a linear or branched C₁₋₆ alkyl or C₆₋₁₀ aryl moieties; wherein R_(B2) independently represents a C₆₋₁₀ aryl or a C₁₋₁₀ alkyl moiety. Advantageously, the oxygen scavenger (d) may be from the class (Ph)₂PR_(B1), wherein R_(B1) independently represents a C₆₋₁₀ aryl moiety optionally further substituted with one or more —C(═O)OH, —C(═O)OR_(B2), or a linear or branched C₁₋₆ alkyl or C₆₋₁₀ aryl moieties; wherein R_(B2) independently represents a C₆₋₁₀ aryl or a C₁₋₁₀ alkyl moiety. Preferably the oxygen scavenger (d) may be from the class (Ph)₂PR_(B1), wherein R_(B1) represents a C₆aryl moiety bearing one or more C(═O)OH or —C(═O)OR_(B2) moieties, wherein R_(B2) independently represents a C₆₋₁₀ aryl or a C₁₋₁₀ alkyl moiety. For example, the oxygen scavenger (d) may be 4-(diphenylphosphino)benzoic acid (4-dppba).

e) Irradiation Light Source

The light source may be any light source known in the art, capable of generating light in the 625-2500 nm region, for example in the range of 625-1500 nm. For example, light emitted from LED bulbs, laser, laser diode, low pressure mercury and argon lamps, fluorescent light systems, electric arc-light sources, high intensity light sources may be used. Advantageously, the light source may generate light in the red region of the light spectrum (i.e., 625-750 nm). For example, light sources that may be used to that effect include LED bulb, laser, laser diode, fluorescent light system, electric arc light source, high intensity (metal halide 3000K, high pressure sodium lamp), Xenon light, Mercury-Xenon light. Advantageously, the light source may generate light in the near-infrared region of the light spectrum (i.e., 700-2500 nm, for example 700-1500 nm). For example, light sources that may be used to that effect include NIR LEDs, NIR lasers, low pressure mercury and argon lamps (696-1704 nm) Tungsten light source, tungsten halogen light source, Nd:Yag laser, Nd:YVO₄, Nd:CidVO₄, Nd:LuVO₄, CO₂ laser. An important advantage of the invention is that photopolymerization can be effected under long wavelength irradiation conditions (i.e., less energetic and safer than UV-type irradiation for example).

Advantageously, the light source is preferably selected as a function of the absorbing dye to be used: most advantageously, the light source may be one that emits light in the wavelength range where the dye most readily absorbs the light to form a dye^(⋅+) radical, which initiates the polymerization process. The absorbance profiles of dyes known to absorb in the red or near infrared range of the light spectrum are known or can be readily determined by running an absorbance vs. wavelength graph. As will be readily apparent throughout the teachings of the present document, if a particular dye exhibits low/moderate absorbance at a given wavelength, one may still proceed with that particular dye at the same given wavelength by increasing the intensity of the light irradiation. This may be done by using a tunable power light source for example, such as commercially available tunable power red to near-infrared light sources.

RED or NIR Dye Absorbance range IR 140 600-900 nm IR 780 >670 nm Indocyanine Green 600-900 nm IR 813 >670 nm S 2265 600-850 nm S 0991 >650 nm Mn—Ph 600-800 nm Dithiolene Nickel 1 >750 nm Chlorophyllin copper 550-700 nm sodium salt

For illustration purposes, if IR 140 is used as absorbing dye, a NIR laser@785 nm may be used.

As discussed above, it is understood that the light source may be a tunable power light source; that is one that is equipped with tunable power, so as be able to adjust the power of the red to near infrared light irradiation, if needed. Such tunable power light source may also be used to determine the light intensity threshold at which a particular dye starts to absorb at any given wavelength, and therefore to fine-tune the wavelength/irradiation intensity that may be used to obtain optimal conditions for polymerization.

f) Polymerizable Component

Advantageously, the photo-initiating composition according to the invention may be used for polymerization reactions that involve at least one polymerizable component selected from:

-   -   (i) an ethylenically unsaturated monomer, the polymerization of         which may be effected by free radical polymerization; and/or     -   (ii) an ethylenically unsaturated monomer or an epoxy-containing         monomer or an oxetane monomer or a vinyl ether containing         monomer or lactide monomer or lactone monomer or caprolactone         monomer; the polymerization of which may be effected by cationic         polymerization.

Advantageously, at least one polymerizable component may be an ethylenically unsaturated monomer, the polymerization of which may be effected by free radical polymerization. As used herein, the term “ethylenically unsaturated monomer” refers to a monomer that contains at least one carbon-carbon double bond. Preferably, ethylenically unsaturated monomers whose polymerization may be effected by free radical polymerization, contains at least one carbon-carbon double bond that is conjugated with an aryl moiety (e.g., phenyl), a carboxyl (C═O) group, or another double bond. Such monomers in this category include for example acrylates—[(ROCO)CHCH₂]—(acrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate, etc. . . .), methacrylates —[(ROCO)C(Me)CH₂]—(methacrylic acid, methyl methacrylic acid, etc. . . .), styrene, ethylene, propylene, N-vinyl acrylamide, N-vinylpyrolidone. For example, at least one polymerizable component may be an acrylate or methacrylate monomer. For example, at least one polymerizable component may be a methacrylate monomer such as (hydroxypropyl)methacrylate (HPMA), 1,4-butanediol dimethacrylate (1,4-BDDMA), 1,6-Bismethacryloxy-2-ethoxycarbonylamino-2,4,4-trimethylhexane (BMATMH) or methacrylate functionalized prepolymers such as UDMA

Advantageously, at least one polymerizable component may be an ethylenically unsaturated monomer or an epoxy-containing monomer or an oxetane monomer or a vinyl ether containing monomer or lactide monomer or lactone monomer or caprolactone monomer; the polymerization of which may be effected by cationic polymerization. Examples of these monomers include vinyl ethers —[ROCHCH₂]—such as vinyl methyl ether, vinyl ethyl ether, vinyl isobutyl ether; and epoxy monomers. As used herein, the term “epoxy-containing monomer” refers to a monomer bearing a moiety comprising an oxirane ring having the structure:

for example

wherein “*” denotes the point(s) of attachment of the oxirane moiety to the rest of the monomer; and R₁ and R₂ independently represent H or a linear or branched C₁₋₁₀ alkyl or C₆₋₁₀ aryl moiety; wherein each of the foregoing aryl moieties may be, individually, further substituted with one or more linear or branched C₁₋₆ alkyl or C₆₋₁₀ aryl moieties. For example, the polymerizable component may be the epoxide-containing monomer (EPDX) having the following structure:

Likewise, as used herein, the term “oxetane-containing monomer” refers to a monomer bearing a moiety comprising an oxetane ring having the structure:

for example

wherein “*” denotes the point(s) of attachment of the oxetane moiety to the rest of the monomer; and R₁ and R2 independently represent H or a linear or branched C₁₋₁₀ alkyl or C₆₋₁₀ aryl moiety; wherein each of the foregoing aryl moieties may be, individually, further substituted with one or more linear or branched C₁₋₆ alkyl or C₆₋₁₀ aryl moieties. For example, at least one polymerizable component may be one of the following oxetane-containing monomers:

Vinyl ether-containing monomers useable in the context of the present invention may be any known Vinyl ether-containing monomers, including commercially available vinyl ether monomers such as: Bis[4-(vinyloxy)butyl] 1,6-hexanediylbiscarbamate, Bis[4-(vinyloxy)butyl] isophthalate, Bis[4-(vinyloxy)butyl] (methylenedi-4,1-phenylene)biscarbamate, Bis[4-(vinyloxy)butyl] succinate, Bis[4-(vinyloxy)butyl]terephthalate, Bis[4-(vinyloxymethyl)cyclohexylmethyl] glutarate, 1,4-Butanediol divinyl ether , 1,4-Butanediol vinyl ether, Butyl vinyl ether, tert-Butyl vinyl ether, 2-Chloroethyl vinyl ether, cis-1,4-Cyclohexanedimethanol divinyl ether, trans-1,4-Cyclohexanedimethanol divinyl ether, Cyclohexyl vinyl ether, Di(ethylene glycol) divinyl ether, Di(ethylene glycol) vinyl ether, Diethyl vinyl orthoformate, Dodecyl vinyl ether, Ethylene glycol vinyl ether, 2-Ethylhexyl vinyl ether, 2-Ethylhexyl vinyl ether, Ethyl- 1-propenyl ether (cis, trans, or mixture thereof), Ethyl vinyl ether, Isobutyl vinyl ether, Phenyl vinyl ether, Propyl vinyl ether Tris[4-(vinyloxy)butyl] trimellitate.

It is to be understood that the photo-initiating composition of the invention may be used for effecting free radical polymerization and/or cationic polymerization of at least one polymerizable component selected from:

-   -   (i) an ethylenically unsaturated monomer, the polymerization of         which may be effected by free radical polymerization; and/or     -   (ii) an ethylenically unsaturated monomer or an epoxy-containing         monomer or an oxetane-containing monomer or a vinyl         ether-containing monomer or lactide monomer or lactone monomer         or caprolactone monomer; the polymerization of which may be         effected by cationic polymerization;         or a mixture of two or more of the above.

As such, the polymerizable component may be a mixture of two or more of ethylenically unsaturated monomers (i), as defined and described generally and in variants herein. For example, the polymerizable component may be a mixture of:

The polymerizable component may be a mixture of two or more monomers (ii), as defined and described generally and in variants herein. For example, a mixture of a vinyl ether monomer and an ethylenically unsaturated monomer polymerizable by cationic polymerization may be used.

The polymerizable component may also be a mixture of at least one monomer (i) and at least one monomer (ii), as defined and described generally and in variants herein. In other words, the polymerizable component may be a mixture of two or more components which are polymerizable via different polymerization mechanisms: free radical polymerization or cationic polymerization, respectively. For example, the polymerizable component may be a mixture of HPMA and EPDX. Other examples include mixtures vinylether/acrylate and vinylether/epoxy.

One important advantage of the three-component photoinitiator compositions described herein is at least two fold:

-   -   (i) they generate free radicals under very mild irradiation         conditions (i.e., under an irradiation intensity of a few W/cm²         or even in the mW/cm² range, in the near infrared region e.g.,         λ=625-2500 nm, for example under near infrared light range         λ=700-2500 nm, in particular in the near infrared light range         λ=700-1500 nm), and     -   (ii) they can initiate free radical promoted cationic         photopolymerization, when an ethylenically unsaturated monomer         or an epoxy-containing monomer or an oxetane-containing monomer         or a vinyl ether-containing monomer or lactide monomer or         lactone monomer or caprolactone monomer; the polymerization of         which may be effected by cationic polymerization, is present.

Accordingly, the use of the three-component photoinitiator compositions of the invention under mild light irradiation conditions allows concomitant free radical and cationic polymerizations to take place when a mixture of monomers with these distinct polymerization mechanisms is used. This allows the preparation of interpenetrated networks of polymers that have different polymerization mechanisms (free radical and cationic), with a single photoinitiator. This is a striking advantage, as compared to existing methods, which require the use of two different polymerization initiators: a photoinitiator for the free radical polymerization, and a cationic initiator for the cationic polymerization. Necessarily, the use of two different initiators, means different initiating times, and thus polymerizations that may go at different speed and/or with different efficiencies, thereby leading to interpenetrated polymer networks far less homogeneous than those obtainable by the photopolymerization method of the invention.

The adsorbing dye a), oxidizing agent b), reducing agent c), polymerizable component f) and irradiation light source may be as defined in any variant described above and herein.

Advantageously, the following proportions of a), b) and c) may be used:

-   -   the adsorbing dye may be used in about 0.01-0.5 wt %, preferably         0.01-0.4 wt %, preferably 0.01-0.3 wt %, more preferably ≤0.25         wt %, still more preferably ≤0.20 wt %, most preferably ≤0.15 wt         %. For example the adsorbing dye may be used in about 0.05 wt %,         0.06 wt %, 0.07 wt %, 0.08 wt %, 0.09 wt %, 0.10 wt %, 0.11 wt         %, 0.12 wt %, 0.13 wt %, 0.14 wt %, 0.15 wt %, 0.16 wt %, 0.17         wt %, 0.18 wt %, 0.19 wt %, 0.20 wt %;     -   the oxidizing agent may be used in about 0.1-5.0 wt %,         preferably 0.5-5.0 wt %, preferably 0.5-4.0 wt %, more         preferably 1-4.0 wt %, still more preferably 2.0-4.0 wt %, most         preferably about 3 wt %. For example the oxidizing agent may be         used in about 0.5 wt %, 1.0 wt %, 1.5 wt %, 2.0 wt %, 2.5 wt %,         3.0 wt %, 3.5 wt %, 4.0 wt %, 4.5 wt %, 5.0 wt;     -   the reducing agent may be used in about 0.1-5.0 wt %, preferably         0.5-5.0 wt %, preferably 0.5-4.0 wt %, more preferably 1.0-4.0         wt %, still more preferably 1.0-3.0 wt %, most preferably about         2 wt %. For example the oxidizing agent may be used in about 0.5         wt %, 1.0 wt %, 1.5 wt %, 2.0 wt %, 2.5 wt %, 3.0 wt %, 3.5 wt         %, 4.0 wt %, 4.5 wt %, 5.0 wt %;         all wt % being expressed based on the total weight of the         composition to be polymerized; i.e. total weight of         polymerizable component f)+total weight of components a), b)         and c) recited above. The oxygen scavenger, if different from         the reducing agent, may be used in a suitable amount         conventionally used in photopolymerization processes to exercise         its oxygen scavenging function.

POLYMERIZATION METHOD

In another aspect, there is provided a method for effecting free radical and/or cationic photopolymerization under a 625-2500 nm light source irradiation condition, for example under a 625-1500 nm light source irradiation, comprising a step of polymerizing at least one polymerizable component selected from:

-   -   (i) an ethylenically unsaturated monomer, the polymerization of         which may be effected by free radical polymerization; and/or     -   (ii) an ethylenically unsaturated monomer or an epoxy-containing         monomer or an oxetane-containing monomer or a vinyl         ether-containing monomer or lactide monomer or lactone monomer         or caprolactone monomer; the polymerization of which may be         effected by cationic polymerization;     -   or a mixture of two or more of the above;         in the presence of a photo-initiating composition as defined and         described generally and in variants herein.

The variants described above, notably for the various components for the photo-initiating composition according to the invention are applicable mutatis mutandis to this section, and will be understood to apply to the polymerization method defined in this section. This includes all the variants described in the “DETAILED DESCRIPTION OF CERTAIN PREFERRED EMBODIMENTS OF THE INVENTION” section of this document, including any one and all variants relating to the a) absorbing dye, b) oxidizing agent, c) reducing agent, d) oxygen scavenger, e) irradiation light source and f) polymerizable component described supra in the present document, and infra in the Exemplification section and accompanying Drawings.

For example, at least one polymerizable monomer is an acrylate or methacrylate whose polymerization is effected by radical polymerization.

For example, at least one polymerizable monomer is a vinyl ester or an epoxide whose polymerization is effected by cationic polymerization.

Advantageously, an interpenetrated network of at least two polymers generated by concomitant free radical and/or cationic polymerizations is prepared by effecting free radical and/or cationic photopolymerization according to the present invention (cf. Discussion supra in section “POLYMERIZABLE COMPONENT”, relating to variants where the polymerizable component may be a mixture of two or more components which are polymerizable via different polymerization mechanisms).

POLYMER

In another aspect, there is provided a polymer material obtainable by a photopolymerization method according to the present invention. Likewise, the variants described above, notably for the various components for the photo-initiating composition according to the invention are applicable mutatis mutandis to this section, and will be understood to apply to the polymer material defined in this section. This includes all the variants described in the “DETAILED DESCRIPTION OF CERTAIN PREFERRED EMBODIMENTS OF THE INVENTION” section of this document, including any one and all variants relating to the a) absorbing dye, b) oxidizing agent, c) reducing agent, d) oxygen scavenger, e) irradiation light source, f) polymerizable component, and polymerization method described supra in the present document, and infra in the Exemplification section and accompanying Drawings.

Advantageously, the polymer material may be obtained by photopolymerizing at least in part an ethylenically unsaturated monomer whose polymerization is effected by free radical polymerization, and an ethylenically unsaturated monomer-or an epoxy-containing monomer whose polymerization is effected by cationic polymerization, according to the mild-light induced photopolymerization according to the invention; to form an interpenetrated network of polymers generated by concomitant free radical and cationic polymerizations.

METHODS AND USES

In another aspect, there is provided the use of a photo-initiating composition as defined and described generally and in variants in the present document in a polymerization reaction. For example, the polymerization reaction may be a radical and/or a cationic polymerization. Likewise, the variants described above, notably for the various components for the photo-initiating composition according to the invention are applicable mutatis mutandis to this section, and will be understood to apply to the methods and uses defined in this section. This includes all the variants described in the “DETAILED DESCRIPTION OF CERTAIN PREFERRED EMBODIMENTS OF THE INVENTION” section of this document, including any one and all variants relating to the a) absorbing dye, b) oxidizing agent, c) reducing agent, d) oxygen scavenger, e) irradiation light source, f) polymerizable component, polymerization method and polymer described supra in the present document, and infra in the Exemplification section and accompanying Drawings.

For example, there is provided a use of a photo-initiating composition, as defined and described generally and in variants herein, wherein the polymerization reaction includes at least one polymerizable component selected from:

-   -   (i) an ethylenically unsaturated monomer, the polymerization of         which may be effected by free radical polymerization; and/or     -   (ii) an ethylenically unsaturated monomer or an epoxy-containing         monomer or an oxetane-containing monomer or a vinyl         ether-containing monomer or lactide monomer or lactone monomer         or caprolactone monomer; the polymerization of which may be         effected by cationic polymerization.

Advantageously, the ethylenically unsaturated monomer whose polymerization is effected by free radical polymerization may be an acrylate or methacrylate.

Advantageously, the monomer whose polymerization is effected by cationic polymerization may be an epoxide, an oxetane, a vinyl ether, a lactide, a lactone or a caprolactone monomer.

In addition, there is provided the use of a photo-initiating composition according to the invention, as defined and described generally and in variants herein, for the preparation of an interpenetrated network of at least two polymers generated by concomitant free radical and/or cationic polymerizations.

SYNTHETIC METHODS

The practitioner has a well-established literature of synthetic organic and inorganic chemistry and polymer chemistry to draw upon, in combination with the information contained herein, for guidance on synthetic strategies, protecting groups, and other materials and methods useful for the synthesis of the photo-initiating compositions and polymers according to the present invention. For example, the reader may refer to the Exemplification section below, and references cited therein for synthetic approaches suitable for the preparation of some of the compositions and polymer materials described herein. The reader may refer for references to references [4] and [5], which relate to phthalocyanine dyes. These are often simple to synthesize with relatively high yields and have been used as commercial pigments and dyes for decades.

COMPOSITE MATERIALS

Advantageously, the method according to the invention can generally be carried out using conventional methods of preparing the above described polymers according to the present invention in a suitable mixing device such as, but not limited to, stirred tanks, dissolvers, homogenizers, microfluidizers, extruders, or other equipment conventionally used in the field. When the polymerization method of the invention is used in the preparation of composites and/or laminated articles, the process may further comprise a step of adding a material/reinforcement designed for this purpose using known methods.

Advantageously, the polymerization method further comprises a step of impregnating composite reinforcements with a mixture of the photo-initiating composition and the at least one polymerizable component according to the invention, in a mold, such as a silicone mold, prior to the application of light source.

Advantageously, the composite reinforcements may be any reinforcing conventionally used in the manufacture and implementation of composite materials. For example, the composite reinforcements may be selected from:

-   -   Glass fibers     -   Carbon fibers     -   Aramid fibers (Kevlar®)     -   Basalt fibers     -   Silica fibers     -   Silicon carbide fibers     -   Polymer fibers     -   Vegetal fibers (hemp, flax . . .)     -   Mineral, metallic or organic fillers (for example gravel, sand,         glass beads, carbonate powder, alumina hydrate powder, steel         powder, aluminum powder, polymer particles, titanium oxide,         alumina, etc . . .)

Advantageously, the composite reinforcements may be selected from glass fibers, carbon fibers, aramid fibers, basalt fibers, silica fibers, polymer fibers (such as polyesters, poly (p-phenylene-2,6 -benzobisoxazole), aliphatic and aromatic polyamides, polyethylene, polymethyl methacrylate, polytetrafluoroethylene), natural fibers (such as nettle, flax or hemp fibers) . . . .

Advantageously, the composite reinforcements may be previously disposed in a mold, and then impregnated by a mixture of the photo-initiating composition and the at least one polymerizable component according to the invention (step(i)), before application of light radiation (step (ii)).

Alternatively, composite reinforcements may be pre-impregnated with a mixture of the photo-initiating composition and the at least one polymerizable component according to the invention. Then the resulting mixture may be deposited/spread evenly over the mold, either manually or using an automated robot, in the case of mass production.

The process may further include a step of adding any other additive conventionally used in the field of resins, composite materials and applications. Examples of suitable additives include:

-   -   pigments, such as colored pigments, fluorescent pigments,         electrically conductive pigments, magnetically shielding         pigments, metal powders, scratch-proofing pigments, organic dyes         or mixtures thereof;     -   light stabilizers such as benzotriazoles or oxalanilides;     -   crosslinking catalysts such as dibutyltin dilaurate or lithium         decanoate;     -   slip additives;     -   defoamers;     -   emulsifiers, especially nonionic emulsifiers such as alkoxylated         alkanols and polyols, phenols and alkylphenols or anionic         emulsifiers, such as alkali metal salts or ammonium salts of         alkanecarboxylic acids, alkanesulfonic acids, alkanol sulfonic         acids or alkoxylated polyols, phenols or alkyl phenols;     -   wetting agents such as siloxanes, fluorinated compounds,         carboxylic monoesters, phosphoric esters, polyacrylic acids or         their copolymers, polyurethanes or acrylate copolymers, which         are commercially available under the trademark MODAFLOW® or         DISPERLON®;     -   adhesion promoters such as tricyclodecan-dimethanol;     -   leveling agents:     -   film-forming adjuvants such as cellulose derivatives;     -   flame retardants;     -   sag control agents such as ureas, modified ureas and/or silicas,     -   rheology control additives such as those described in patent         documents WO 94/22968 [7], EP0276501A1 [8], EP0249201A1 [9], and         WO 97/12945 [10];     -   crosslinked polymeric microparticles, as described for example         in EP0008127A1 [11];     -   inorganic phyllosilicates such as aluminum magnesium silicate,         magnesium sodium silicates or magnesium fluoride sodium lithium         phyllosilicates of montmorillonite type;     -   silicas such as aerosils® silicas;     -   flatting agents such as magnesium stearate; and/or     -   tackifiers.

Mixtures of at least two of these additives are also suitable in the context of the invention.

As used herein, the term “tackifier” refers to polymers which increase the tack properties, that is to say, the intrinsic viscosity or self-adhesion, the compositions so that, after a slight pressure a short period, they adhere firmly to surfaces.

In another aspect, the invention provides articles obtainable by a polymerization process according to any one variant of the inventive method, as defined and described generally and in variants herein.

The present invention offers many advantages, including:

-   -   Red to Near-infrared wavelengths induce a deeper penetration in         the material to be polymerized. As shown in FIG. 1 , the greater         the wavelength: the less the light is diffused by the charges in         the material. Thus, the curing of filled materials with NIR         source is enhanced compared to curing with UV or visible light;         This allows polymerization of much thicker samples/polymeric         materials than conventional UV-induced or visible light-induced         photopolymerization;     -   The process is safer than widely used UV-curing processes;     -   Red-based and NIR-based photoinitiator systems according to the         invention are more efficient (higher conversion rate and/or         photopolymerization rate);     -   Cost efficiency (the process can be carried out at room         temperature and under milder light irradiation than conventional         UV-based of visible light-induced photoinitiator systems;     -   Environmentally friendly (no solvent necessary);     -   Possibility of applications in the medical field, notably due to         the use of Red to near-infrared wavelengths (much safer than UV         wavelengths). Existing laser sources in the dermatologic field         may be used for that purpose.

Other advantages may also emerge to those skilled in the art upon reading the examples below, with reference to the attached figures, which are provided as nonlimiting illustrations.

EQUIVALENTS

The representative examples that follow are intended to help illustrate the invention, and are not intended to, nor should they be construed to, limit the scope of the invention. Indeed, various modifications of the invention and many further embodiments thereof, in addition to those shown and described herein, will become apparent to those skilled in the art from the full contents of this document, including the examples which follow and the references to the scientific and patent literature cited herein. It should further be appreciated that the contents of those cited references are incorporated herein by reference to help illustrate the state of the art.

The following examples contain important additional information, exemplification and guidance that can be adapted to the practice of this invention in its various embodiments and the equivalents thereof.

EXEMPLIFICATION

The polymer materials and compositions of this invention and their preparation can be understood further by the examples that illustrate some of the processes by which these polymer materials and compositions are prepared or used. It will be appreciated, however, that these examples do not limit the invention. Variations of the invention, now known or further developed, are considered to fall within the scope of the present invention as described herein and as hereinafter claimed.

SUMMARY

In the Examples that follow is illustrated the use of a three-component photo-initiating composition according to the invention for the NIR photopolymerization of methacrylates. Specifically, the exemplary photo-initiating composition comprises 1) a dye used as a photosensitizer that absorbs in the NIR range, 2) a iodonium salt as oxidizing agent and 3) a phosphine compound as reducing agent and concomitant oxygen scavenger to prevent against the polymerization inhibition due to the presence of oxygen.

Phosphine have been shown to reduce oxygen inhibition, however, they have only been reported in such capacity for polymerization with visible light and not with NIR sources. This is therefore to our knowledge the first report of the use of phosphine compounds in NIR-induced photopolymerization and photoinitiator systems.

Incidentally, near infrared (NIR) photo-initiating systems for the photopolymerization of methacrylates monomers is still relatively rare in the literature. Photopolymerization under NIR light is challenging due to the low energy, but if successful, presents several advantages. For example, this lower energy wavelength can be safer than UV-light that is currently the dominant light source represented in the literature for photocuring. Secondly, NIR allows a deeper penetration of the light and therefore a more complete curing, especially for polymerization in presence of fillers.

Several NIR absorbing dyes are presented and studied in the Examples that follow, such as borates and phthalocyanines. Notably, system using borate dyes resulted in methacrylate monomer conversion over 80% under air.

Three types of irradiation system are presented: low power LED @660 nm and @780 nm and a high power laser @785 nm.

EXAMPLE 1: MATERIALS AND METHODS 1) Exemplary Synthesis of Cyanine Absorbant Borate Dyes IR-140 Borate

All reagents and solvents for the synthesis of IR-140 borate (Scheme 1) were purchased from Aldrich or Alfa Aesar and used as received without further purification. 5,5′-Dichloro-11-(diphenylamino)-3,3′-diethyl-10,12-ethylene- thiatricarbocyanine perchlorate (IR140) was purchased from Aldrich. Mass spectroscopy was performed by the Spectropole of Aix-Marseille University. ESI mass spectral analyses were recorded with a 3200 QTRAP (Applied Biosystems SCIEX) mass spectrometer. The HRMS mass spectral analysis was performed with a QStar Elite (Applied Biosystems SCIEX) mass spectrometer. Elemental analyses were recorded with a Thermo Finnigan EA 1112 elemental analysis apparatus driven by the Eager 300 software. ¹H and ¹³C NMR spectra were determined at room temperature in 5 mm o.d. tubes on a Bruker Avance 400 spectrometer of the Spectropole: ¹H (400 MHz) and ¹³C (100 MHz). The ¹H chemical shifts were referenced to the solvent peak CDCl₃ (7.26 ppm), DMSO (2.49 ppm) and the ¹³C chemical shifts were referenced to the solvent peak CDCl₃ (77 ppm), DMSO (49.5 ppm). Lithium triphenylbutylborate was synthesized as previously reported in the literature, without modifications and obtained in similar yields [12]. The soft salt was synthesized as previously reported in the literature, by using a biphasic mixture of CHCl₃/water and THF to act as a phase transfer agent. The soft salt (the organic salt) was recovered in the organic phase, the inorganic one in the aqueous phase [13].

Lithium triphenylbutylborate (236 mg, 0.770 mmol, 1.2 eq.) in water (20 mL) was added to a solution of 5,5′-dichloro-11-(diphenylamino)-3,3′-diethyl-10,12-ethylene-thiatricarbocyanine perchlorate (500 g, 0.642 mmol, 1 eq.) in a mixture of CHCl₃ (100 mL) and THF (20 mL). The solution was stirred at room temperature while being protected from light for 1 hour and then set aside for 10 minutes. THF was removed under reduced pressure (still while protecting the solution from light) and the solution was transferred in a separating funnel (covered with aluminum foil). The organic phase was separated, dried over magnesium sulfate and the solvent removed under reduced pressure. Addition of THF (2 mL) followed by pentane precipitated a solid that was filtered off, washed several times with pentane and dried under vacuum. HRMS (ESI MS) m/z: theor: 679.7428 found: 679.7426 (M+ detected); HRMS (ESI MS) m/z: theor: 299.2375 found: 299.2377 (M- detected); Anal. Calc. for C61H58BC12N3S2: C, 74.8; H, 6.0; N, 4.3 Found: C, 74.6, H, 6.1; N, 4.4%.).

IR-780 Borate

All reagents and solvents for the synthesis of IR-780 borate (Scheme 1) were purchased from Sigma-Aldrich and used as received without any further purification. Lithium triphenylbutylborate was synthesized as previously reported in the literature, without modifications and obtained in similar yields [12]. Lithium triphenylbutylborate (45.9 mg, 0.15 mmol, 1.2 eq.) in water (20 mL) was added to a solution of 2-[2-[2-Chloro-3-[(1,3-dihydro-3,3-dimethyl-1-propyl-2H-indol-2- ylidene)ethylidene]-1-cyclohexen-1-yl]ethenyl]-3,3-dimethyl-1-propylindolium iodide (100 mg, 0.18 mmol, 1 eq.) in a mixture of CHCl₃ (100 mL) and THF (20 mL). 2-[2-[2-Chloro-3-[(1,3-dihydro-3,3-dimethyl-1-propyl-2H-indol-2-ylidene)ethylidene]-1-cyclohexen-1-yl]ethenyl]-3,3-dimethyl-1-propylindolium iodide is abbreviated “IR-780 iodide” in the present paper. The solution was stirred at room temperature during 1 hour in a round-bottom flask covered with aluminum foil. The organic phase was then removed under pressure. CHCl₃ (10mL) was added in the round-bottom flask. The solution was transferred in a separating funnel (covered with aluminum foil) to separate the organic phase which were then dried over magnesium sulfate. The solvent left were removed under reduced pressure.

2) Commercial Absorbing Dyes

IR-780 iodide, IR-140, Manganese(II) Phthalocyanine, Dithiolene Nickel, IR-813 p-toluenesulfonate, IR 783, and chlorophyllin copper sodium salt were purchased from Sigma-Aldrich. Indocyanine Green was purchased from TCI Chemicals. No further purification was made.

3) Other Chemical Compounds Polymerizable Components

A mixture (also referred to herein as “Mix-MA”) of 33 wt % of (hydroxypropyl)methacrylate (HPMA), 33 wt % of 1,4-butanediol dimethacrylate (1,4-BDDMA) and 33 wt % of a methacrylate functionalized prepolymer was used as polymerizable component. Mix-MA was obtained from Hilti GmbH.

Iodonium Salt

Bis-(4-tert-butylphenyl)-Iodonium hexafluorophosphate (Ar₂I⁺/PF₆ ⁻ or also Speedcure 938), obtained from Lambson, was used as oxidizing agent.

Phosphine Compound

4-(diphenylphosphino)benzoic acid (4-dppba), purchased from Sigma-Aldrich, was used as reducing agent and concomitant oxygen scavenger. No further purification was made.

Silica beads obtained from Dentsply GmbH were used as fillers.

4) Irradiation Sources

Several types of irradiation sources were used throughout the Examples that follow: NIR LED@660 nm (with a power of 80 mW/cm²), NIR LED@780 nm (with a power of 130 mW/cm²) and a NIR laser@785 nm with tunable power (from OW to 2.55 W/cm²) from ThorLabs.

5) Photopolymerization Experiments

The photosensitive formulations (mixture of polymerizable component(s) and photo-initiating composition according to the present invention) were deposited on a polypropylene film (thickness=1.4 mm) and polymerized under air by irradiation with LED or laser. The conversion was followed by real time Fourier transformation infrared (FTIR) spectroscopy using a JASCO 4600. The double bond C═C content of Mix-MA was measured at 6100-6220 cm⁻¹ (FIG. 2 ). Specific reaction conditions for each photopolymerization experiments are given in the figures caption. For all experiments, recording of the FTIR spectra was initialized a minimum of 10 seconds prior to the irradiation, to obtain a baseline for comparison.

EXAMPLE 2. PHOTO-INITIATING COMPOSITION COMPRISING IR-140 BORATE AS ABSORBING DYE 1. Low NIR Light Intensity

IR-140 borate has been used in this example to initiate the free radical polymerization upon irradiation at 785 nm (400 mW/cm²) using a laser. The photo-initiating composition used in this Example was based on a three-component formulation containing IR-140 borate (as a dye)/Ar₂I⁺/PF₆ ⁻/4-dppba. It was shown to exhibit a high polymerization rate under exposure to laser (FIG. 3 ). The final monomer conversion was roughly 50-60% and the final polymer was tack-free at the surface. When omitting one of the two additives (Ar₂I⁺/PF₆ ⁻ or 4-dppba) or when irradiating the monomer alone, no photopolymerization took place. The polymerization efficiency as compared to the different control formulations is outlined in Table 1. When increasing the light source energy from LED at 400 mW/cm² (experiment 3, in FIG. 3 ) to laser at 2.55 W/cm² (experiment 5, in FIG. 3 ) we observe that the conversion was twice as fast.

TABLE 1 Photopolymerization results of Mix-MA under air in the presence, or absence, of different additives under exposure to Laser@785 nm (400 mW/cm²) during 1000 s; thickness = 1.4 mm: (+) efficient polymerization or (−) no polymerization observed. Power System (W/cm²) Polymerization Monomer (Mix-MA) alone 0.4 − IR-140 borate 0.4 − IR-140 borate/4-dppba 0.4 − IR-140 borate/Ar₂I⁺/PF₆ ⁻ 0.4 − IR-140 borate/4- 0.4 + dppba/Ar₂I⁺/PF₆ ⁻

2. Higher NIR Light Intensity

The power of the laser at 785 nm used in this experiment can easily be tuned between 0 to 2.55 W/cm². The effect of the laser power on the polymerization rate has been characterized for a photo-initiating composition comprising IR-140 borate, 4-dppba and Ar₂I⁺/PF₆ ⁻ (FIG. 4 ). By increasing the power of the laser, the polymerization rate and final conversion both increased. Regardless of the laser power that was used, the final polymers obtained were tack-free. The incubation time at the beginning of the polymerization was also reduced by increasing the power of the laser.

It is important to note that at max power, 2.55 W/cm², the polymerization starts almost as soon as the laser is turned on and the final monomer conversion is greater than 80%. The data in Table 2 supports that polymerization is not possible unless a photo-initiating composition according to the invention is used (cf. last entry in Table 2).

TABLE 2 Photopolymerization results of Mix-MA under air in the presence of different additives under exposure to Laser@785 nm (2.55 W/cm²) during 1000 s; thickness = 1.4 mm; (+) polymerization/evaporation observed or (−) polymerization/evaporation not observed. Power System (W/cm²) Polymerization Monomer (Mix-MA) alone 2.55 − IR-140 borate 2.55 − IR-140 borate/4-dppba 2.55 − IR-140 borate/Ar₂I⁺/PF₆ ⁻ 2.55 − IR-140 borate/4- 2.55 + dppba/Ar₂I⁺/PF₆ ⁻

3. Photopolymerization Formulation Using Fillers

Fillers are often sued in photopolymerization curing and therefore their use has been explored using the photo-initiating composition according to the invention. In general, when added to a formulation to be polymerized, the fillers decrease the penetration of the light rendering it more difficult for the photopolymerization process to take place. Using, the three-component photo-initiating composition according to the invention, the photopolymerization has been followed by RT-FTIR (FIG. 5 ). Weight percentage of fillers ranging from 25 wt % to 75 wt % resulted in tack-free polymers and final monomer conversion between 60% and 80%. The polymerization was not significantly slower with the addition of fillers. The photopolymerization of thicker sample with 75 wt % fillers was also possible (FIG. 5 (C)). A sample of 1 cm high was successfully polymerized in under 30 seconds and a tack-free surface has been obtained.

EXAMPLE 3. PHOTO-INITIATING COMPOSITION COMPRISING OTHER RED-NIR ABSORBING DYES

The photo-initiating composition “dye/Ar₂I⁺/4-dppba” according to the invention has also been characterized with a variety of other dyes absorbing in the Red-NIR range. Commercially available dyes were compared to borate dyes and novel silicon Pc based dyes. Three different irradiation configurations were used: Laser@785 nm at 400 mW and at 2.55 W and LED@660 nm. All polymerization results have been summarized in Tables 3 and 4.

At 660 nm, IR-140 borate resulted in effective polymerization, whereas polymerization was less optimal for IR780 iodide and Indocyanine Green (cf. FIG. 6A). The polymer obtained with IR-140 was tack-free at the surface.

At 785 nm, the result is correlated to the laser intensity:

At 400 mW/cm² (FIG. 6B), IR-140 borate has better performance in terms of speed and of final conversion. However, both Indocyanine Green and IR-140 borate result in polymer formation. With Indocyanine Green, the final conversion is low and the polymer is liquid at the surface whereas with IR-140, the polymer is tack-free and the polymerization faster. IR-813 p-toluene sulfonate was also tested (results not shown in FIG. 6B), but resulted in no polymerization at that particular laser intensity.

At 785 nm and 2.55 W/cm², IR-140 borate still resulted in the faster polymerization (FIG. 6C). However, Indocyanine Green and IR-813 p-toluene sulfonate gave the same final conversion as IR-140 borate. For these three dyes, the polymer is tack-free at the surface. There is also polymerization at this wavelength and this intensity for IR-780 borate, Dithiolene Nickel, chlorophyllin copper sodium salt and Manganese Phthalocyanine.

TABLE 3 Photopolymerization results of Mix-MA under air in the presence of dye/Ar₂I⁺/PF₆ ⁻/4-dppba (0.1 w %/3 w %/2 w %) under exposure to LED@660 nm; thickness = 1.4 mm; (+) efficient polymerization or (−) no polymerization observed. Dye Light source Polymerization IR-140 borate LED@660 nm +++ Indocyanine Green LED@660 nm + IR-780 iodide LED@660 nm +

TABLE 4 Photopolymerization results of Mix-MA under air in the presence of dye/Ar₂I⁺/PF₆ ⁻/4-dppba (0.1 w %/3 w %/2 w %) under exposure to Laser@785 nm; thickness = 1.4 mm; (+) efficient polymerization or (−) no polymerization observed. Power Dye (W/cm²) Polymerization IR-140 borate 2.55 + Indocyanine Green 2.55 + IR-780 borate 2.55 + IR813 p-toluenesulfonate 2.55 + Manganese (II) Phthalocyanine 2.55 + Dithiolene nickel 2.55 + Chlorophyllin copper salt 2.55 + IR-140 borate 0.4 + Indocyanine Green 0.4 + IR813 p-toluenesulfonate 0.4 −

2.1 Influence of the Counter-Ion

Two dyes have been compared with two different counter-ions: IR-780 iodide/IR-780 borate and IR-140 perchlorate/IR-140 borate. For IR-780 iodide, some polymerization was observed at 660 nm; whereas with IR-780 borate, a tack-free polymer was obtained with a final conversion of roughly 70% at 785 nm. For IR-140, there was polymerization with both counter-ions but the polymerization was faster with the borate than with the perchlorate and the final conversion was higher (FIG. 7 ).

COMPARATIVE EXAMPLE: IR-140 BORATE VS. S 2265 CYANINE FOR NIR PHOTOPOLYMERIZATION

Cyanine dye S 2265 has recently been reported as effecting polymerization of UDMA monomer when combined with a second cyanine dye, S 0991). When S 2265 was used without S 0991, the melting is less efficient but crosslinking was still observed.

In the present comparative example, S 2265 was used for the first time with a phosphine in a three-component photo-initiating composition “iodonium salt/phosphine/dye” according to the invention, to initiate free radical polymerization of Mix-MA upon irradiation at 785 nm (400 mW/cm²).

FIG. 8 shows the photopolymerization profiles of Mix-MA under air (methacrylates function conversion vs. irradiation time) in the presence of Ar₂I⁺/PF₆ ⁻ (3 w %), 4-dppba (2 w %) and (1) IR-140 borate (0.1 w %) or (2) S2265 (0.1 w %) under exposure to Laser@785 nm, 2.55 W/cm²; thickness=1.4 mm. The irradiation started at t=17 s.

As seen on FIG. 8 , the polymerization was fast and resulted in a final conversion of roughly 80%. The resulting polymer that was tack-free at the surface. It is observed that the color of the resin changes before and after polymerization: the formulation is green before irradiation and becomes brown after irradiation. IR-140 borate lead to a faster and a higher conversion than S2265.

Photopolymerization using S 2265 without phosphine has been explored as comparative example. Under the same irradiation conditions as above, no polymerization was achieved after 800 s of irradiation at 785 nm (400mW/cm²). However, color change from green to brown was observed. We believe that the difference observed between the lack of polymerization in the comparative example described above, and the low polymerization observed with the S 2265/S 0991 dye combination in the literature is most likely due to the choice of monomer. The Mix-MA monomer mixture used in the comparative example gave a significantly less viscous liquid compared to the UDMA/S2265/S0991 mixture used in the literature. Therefore during the stirring of the reaction mixture in the comparative example, much more oxygen is dissolved in the reaction mixture, which in turn inhibits the free radical polymerization process. The phosphine present in the photo-initiating composition used in the comparative example serves to overcome this inhibition. This shows the synergistic effect of the tri-association dye+Ar₂I⁺/PF₆ ⁻+4-dppba (4-dppba favors the polymerization efficiency).

Incidentally, we can observe that IR-140 borate provides a more efficient photo-initiating system in presence of Ar₂I⁺/4-dppba than S2265.

EXAMPLE 4. PHOTO-INITIATING COMPOSITION COMPRISING AN AMINE-BASED REDUCING AGENT

The Examples that precede demonstrate the high performances for methacrylate resins using three-component photoinitiating systems according to the present invention, using a phosphine-based compound as reducing agent for regenerating the dye (i.e., three-component system: Dye/Iodonium/phosphine).

The present Example aims at illustrating a three-component photo-initiating composition according to the invention, of the type “dye/Iodonium/amine-based reducing agent”. Specifically, Example 2 was repeated with a variety of dyes and two different amines as reducing agent for regenerating the dye.

Experiments were performed using methacrylate resin Mix-MA as polymerizable component.

TABLE 5 Photoinitiating composition Polymerizable Dye Oxidizing agent Reducing agent component 0.1% w/w 3.0% w/w 2.0% w/w Mix-MA IR 783 Ar₂I⁺/PF₆ ⁻ DABA NPG Mix-MA IR 813 Ar₂I⁺/PF₆ ⁻ DABA NPG Mix-MA Indocyanine green Ar₂I⁺/PF₆ ⁻ DABA NPG Mix-MA IR 780 Ar₂I⁺/PF₆ ⁻ DABA NPG Mix-MA IR 140 Ar₂I⁺/PF₆ ⁻ DABA NPG

% w/w are expressed with respect to the total weight Mix-MA+dye+oxidizing agent+reducing agent.

IR 783, IR 813 and indocyanine green are commercial dyes and were used as such, while IR 780 and IR 140 were prepared by ion exchange with a borate salt (i.e., IR-780 borate and IR 140 borate were used in this experiment).

Mix-MA: mixture of 33 wt % of (hydroxypropyl)methacrylate (HPMA), 33 wt % of 1,4-butanediol dimethacrylate (1,4-BDDMA) and 33 wt % of a urethane dimethacrylate monomer (UDMA).

The polymerization profiles of methacrylate functions were followed by Real-time Fourier transformed infrared spectroscopy (RT-FTIR) experiments for thick samples (1.4 mm), under air. The comparative efficiency of the different NIR dyes in photoinitiating system (PS/Iodonium salt/amines) is illustrated in FIG. 9 . It can be observed in FIG. 9A that a rather good polymerization efficiency in terms of methacrylate final function conversion (FC˜90%) but also good rate of polymerization when using NPG as amine. As shown in FIG. 9B, the systems based on DABA as amine afforded also excellent conversions with different dyes where full final conversions are reached after 100 s of irradiation with the diode laser@785 nm (I=2.5 W/cm²).

The stability upon storage in dark conditions and at room temperature has been also particularly investigated in order to find the best systems for final applications. The experiments show that the photoinitiating ability of IR 780 and IR 783 did not significantly decrease upon storage, thereby demonstrating the stability of the proposed dyes/Iodonium/amines (NPG or DABA) based photoinitiating systems in the photocurable formulations. Dye-based formulations can therefore be stored for some months.

CONCLUSION

The Examples that precede illustrate the efficacy of a three-component photo-initiating composition according to the invention, for example for NIR curing of methacrylate monomers. Radical photopolymerization of methacrylates using two wavelengths of irradiation (660 nm and 785 nm) was successfully initiated by several types of absorbing dyes, including novel silicon phthalocyanine based dyes and borate-dyes. The synergistic effect associated with the combination absorbing dye/oxidizing agent/reducing agent as described generally in the present document has been illustrated with various combinations of dyes/iodonium salt/phosphine as well as dyes/iodonium salt/amine and has been proved as a very efficient photo-initiating system. The system successfully polymerized with only 400 mW.

The red to NIR curing technology described herein relies on the use of a red to NIR absorbing dye which, combined with a particular selection of additives, affords very reactive three-component systems under red to NIR irradiation. The red to NIR curing technology of the present invention can offer an attractive alternative to existing UV/visible systems. The performances are particularly high for thick samples which require a fast curing.

While we have described a number of embodiments of this invention, it is apparent that our basic examples may be altered to provide other embodiments that utilize the catalysts and methods of this invention. Therefore, it will be appreciated that the scope of this invention is to be defined by the appended claims rather than by the specific embodiments that have been represented by way of example.

REFERENCES [1] Lalevée, J.; Fouassier, J. -P. Dyes and Chomophores in Polymer Science; John Wiley & Sons, Inc., 2015.

[2] Karatsu, T.; Yanai, M.; Yagai, S.; Mizukami, J.; Urano, T.; Kitamura, A. Evaluation of Sensitizing Ability of Barbiturate-Functionalized Non-Ionic Cyanine Dyes; Application for Photoinduced Radical Generation System Initiated by near IR Light. Journal of Photochemistry and Photobiology A: Chemistry 2005, 170 (2), 123-129 DOI: 10.1016/j.jphotochem.2004.08.010. [3] Schmitz, C.; Halbhuber, A.; Keil, D.; Strehmel, B. NIR-Sensitized Photoinitiated Radical Polymerization and Proton Generation with Cyanines and LED Arrays. Progress in Organic Coatings 2016, 100, 32-46 DOI: 10.1016/j.porgcoat.2016.02.022. [4] Dahlen, M. A. The Phthalocyanines A New Class of Synthetic Pigments and Dyes. Ind. Eng. Chem. 1939, 31 (7), 839-847 DOI: 10.1021/ie50355a012 [5] Torre, G. de la; Claessens, C. G.; Torres, T. Phthalocyanines: Old Dyes, New Materials. Putting Color in Nanotechnology. Chem. Commun. 2007, 0 (20), 2000-2015 DOI: 10.1039/B614234F. [6] Melville, O. A.; Lessard, B. H.; Bender, T. P. Phthalocyanine-Based Organic Thin-Film Transistors: A Review of Recent Advances. ACS Appl. Mater. Interfaces 2015, 7 (24), 13105-13118 DOI: 10.1021/acsami.5b01718

[7] WO 94/22968 [8] EP0276501A1 [9] EP0249201A1 [10] WO 97/12945 [11] EP0008127A1

[12] Hu, S.; Sarker, A. M.; Kaneko, Y.; Neckers, D. C. Reactivities of Chromophore-Containing Methyl Tri-N-Butylammonium Organoborate Salts as Free Radical Photoinitiators: Dependence on the Chromophore and Borate Counterion. Macromolecules 1998, 31 (19), 6476-6480 DOI: 10.1021/ma980616x. [13] Dumur, F.; Nasr, G.; Wantz, G.; Mayer, C.; Dumas, E.; Guerlin, A.; Miomandre, F.; Clavier, G.; Bertin, D.; Gigmes, D. Cationic Iridium Complex for the Design of Soft Salt-Based Phosphorescent OLEDs and Color-Tunable Light-Emitting Electrochemical Cells. Organic Electronics 2011, 12, 1683-1694 DOI: 10.1016/j.orge1.2011.06.014 [14] Tian, Y.-P.; Zhang, X.-J.; Wu, J.-Y.; Fun, H.-K.; Jiang, M.-H.; Xu, Z.-Q.; Usman, A.; Chantrapromma, S.; Thompson, L. K. Structural Diversity and Properties of a Series of Dinuclear and Mononuclear copper(II) and copper(I) Carboxylato Complexes. New J. Chem. 2002, 26 (10), 1468-1473 DOI: 10.1039/B203334H. [15] Tian, Y.-P.; Zhang, X.-J.; Wu, J.-Y.; Fun, H.-K.; Jiang, M.-H.; Xu, Z.-Q.; Usman, A.; Chantrapromma, S.; Thompson, L. K. Structural Diversity and Properties of a Series of Dinuclear and Mononuclear copper(II) and copper(I) Carboxylato Complexes. New J. Chem. 2002, 26 (10), 1468-1473 DOI: 10.1039/B203334H 

1. A photo-initiating composition comprising: (a) an absorbing dye that is an electron donor when exposed to a light source in the red to near infrared; (b) an oxidizing agent for a polymerization reaction that is capable of generating free radicals and/or cation ions by electron transfer from the absorbing dye when exposed to a light source in the red to near infrared; (c) a reducing agent for regenerating the absorbing dye; and (d) optionally, an oxygen scavenger.
 2. The photo-initiating composition according to claim 1, wherein the absorbing dye is selected from cyanine, phthalocyanine, dithiolene and porphyrin dyes.
 3. The photo-initiating composition according to claim 1, wherein the oxidizing agent is an onium salt of formula ((R_(A))₂I⁺X_(A) ⁻ or (R_(A))₃S⁺X_(A) ⁻; wherein each occurrence of R_(A) independently represents a C₆₋₁₀ aryl or a C₁₋₁₀ alkyl moiety; wherein the aryl moiety may be, individually, further substituted with one or more linear or branched C₁₋₆ alkyl or C₆₋₁₀ aryl moieties; and wherein X_(A) ⁻ represents a counterion.
 4. The photo-initiating composition according to claim 1, wherein the onium salt is:


5. The photo-initiating composition according to claim 1, wherein the reducing agent c) and the oxygen scavenger d) are one and the same compound.
 6. The photo-initiating composition according to claim 1, wherein the reducing agent is selected from a phosphine compound and an amine compound.
 7. (canceled)
 8. (canceled)
 9. (canceled)
 10. (canceled)
 11. (canceled)
 12. (canceled)
 13. A method for effecting free radical and/or cationic photopolymerization under red to near infrared irradiation condition, comprising the step of polymerizing at least one polymerizable component selected from: (i) an ethylenically unsaturated monomer, the polymerization of which may be effected by free radical polymerization; and/or (ii) an ethylenically unsaturated monomer or an epoxy-containing monomer or an oxetane monomer or a vinyl ether containing monomer or lactide monomer or lactone monomer or caprolactone monomer; the polymerization of which may be effected by cationic polymerization; in the presence of the photo-initiating composition of claim
 1. 14. The method according to claim 13, wherein at least one polymerizable monomer is an acrylate or methacrylate whose polymerization is effected by free radical polymerization.
 15. The method according to claim 13, wherein at least one polymerizable monomer is a vinyl ester or an epoxide whose polymerization is effected by cationic polymerization.
 16. The method according to claim 13, wherein an interpenetrated network of at least two polymers generated by concomitant free radical and/or cationic polymerizations is prepared by effecting free radical and/or cationic photopolymerization.
 17. A polymer obtained by a method according to claim
 13. 